Fire-resistant cellulose-bitumen roofing sheet and method of manufacturing

ABSTRACT

Bitumen-impregnated cellulose fiber sheets include on one of their main surfaces, an adhesive primer layer, and, deposited on this adhesive primer layer, a fireproof coating including expandable graphite. In a preferred embodiment of the invention, the expandable graphite has a trigger temperature lower than 300° C. and the layer of expandable graphite corresponds to a dry matter basis weight of 80 to 140 g/m2. The sheets have a fire resistance fulfilling in particular the European Standard EN 13 501-5. They are mainly intended to be used as covering material, and in particular, as roof covering material.

FIELD OF THE INVENTION

The present invention generally relates to fire-resistant,bitumen-impregnated cellulose fiber sheets and their method ofmanufacturing. Said sheets are mainly intended to be used as coveringmaterial, and in particular, as roof covering material.

PRIOR ART

Bitumen-impregnated cellulose fiber sheets are well known by the oneskilled in the art. They are generally manufactured from recycled paperand are rectangular in shape. Conventionally, the recycled paper issubjected to a processing step for removing the non-cellulosic elements,such as staples for example, and to a defibration step, before forming apaper pulp that will be applied on a wire, then let drain andcalibrated. It is possible to add other elements to the pulp, such aspigments for example, in order to obtain colored cover sheets, adaptedto the architectural environment. The cellulose fiber pulp may becorrugated by means of a machine as described in the patent FR 2,496,551or in the patent application EP 0,844,071, so as to obtain rectangularsheets whose corrugations are parallel to the two edges of the length.After drying, a cellulose fiber sheet is obtained, which may be cut atthe desired size. The sheets then are soaked in bitumen, then cooled andpossibly coated with a layer of paint.

The bitumen-impregnated cellulose fiber sheets are materials offeringmany advantages for the field of construction and renovation. Suchsheets are light-weight, resistant, ultra-flexible, easy to install, andcheap. Their flexibility allows them to adapt to the slight deformationsinherent to old woodworks. This is an important characteristic forbuilding renovation. Their light-weight allows them to be installed on alight woodwork. The absence of a high additional load therefore limitsthe structure reinforcements often required for renovation works.Cutting and drilling such sheets require only very simple tools, such ashammer and saw.

The bitumen-impregnated cellulose fiber sheets are thus very widely usedin the field of construction and renovation. However, their lowresistance to an external fire poses a real problem regarding thesecurity standards imposed by the national and internationalauthorities, and in particular those imposed by the European Commission.Indeed, such standards are in constant evolution and the requirementsimposed are more and more severe.

Therefore, there exists a need for improving the fire resistance of thebitumen-impregnated cellulose fiber sheets.

To provide fire resistance to a material, it is known to cover it withan expandable graphite-based coating. Expandable graphite is an intumescent agent that, after exposure to fire, expanses and creates anisolating barrier.

The U.S. Pat. No. 6,436,510 describes cellulose fiber sheets having afire-resistant coating comprising expandable graphite and athermoplastic or thermosetting polymer. Once coated with the polymericbinder and the expandable graphite, the cellulose fiber sheets are thencoated with bitumen and shaped as flat shingles that can be used as roofcovering materials.

Still in the field of construction, the patent US 2011/011021 describescotton fiber plates. The cotton fibers are covered with expandablegraphite by means of a mechanical-bond and/or chemical-bond binder. Thebinder used may be any thermoplastic polymer capable of forming a filmafter drying. Further, polyacrylates, epoxy resins, polyvinyl acetateresins, polyurethanes or styrene-based thermoplastic rubbers arementioned. The plates coated with the fireproof layer may be latercoated with modified bitumen and may thus serve as roof coveringmaterial.

The patent application US 2005/0145139 describes fireproof coatingsimilar to those mentioned hereinabove. This coating is prepared from acomposition comprising at least one polymer binder of same nature thanthose used in the U.S. Pat. No. 6,436,510, particles of expandablegraphite, a vector such as water or a hydrocarbon solvent, according tothe nature of the polymer binder, and a pigment such as, for example,titanium dioxide, calcium carbonate, or borates. The coating is thendried at the temperature of conservation of said material, which mayfurther be a modified bitumen or shingles. An additional external layermay be applied to protect the coating from environmental factors such asrain or wind.

Among the patents or patent applications relating to the use ofexpandable graphite-based coatings for improving the fire resistance ofcellulosic materials, the WO 2004/099491, U.S. Pat. No. 5,686,669 andU.S. Pat. No. 6,084,008 may be mentioned. One of the applications aimedat by the two latter patents is roofing materials.

However, the literature describes no fireproof coating forbitumen-impregnated cellulose fiber sheets. Now, as mentioned above,these sheets offer many advantages in the field of construction buttheir low fire-resistance does not fulfill the standards imposed by theEuropean authorities.

Therefore, there exists a need for improving the fire resistance of thebitumen-impregnated cellulose fiber sheets.

DETAILED DESCRIPTION OF THE INVENTION

One object of the present invention is thus to improve the fireresistance of bitumen-impregnated cellulose fiber sheets, so as tofulfill in particular the European Standard EN 13501-5.

The European Standard EN 13501-5, described in more details in theexamples offire-resistance testing, defines the criteria that must bemet by the roofs subjected to an external fire, and allows for aclassification of roofs as a function of their fire resistance.

Surprisingly, the applicant has discovered that, to form a sufficientlyfire-resistant layer according to the European Standard EN 13501-5, theexpandable graphite, which is the most used fire-retardant agent in thefield of covering materials, had to be deposited through dry deposition,preferably through fluidized bed spray deposition or through hopperdeposition, on an adhesive primer layer. The conventional methods of theprior art, such as spraying the expandable graphite in suspension inwater ora dispersion of the expandable graphite in a polymer binder, donot operate because such methods do not allow obtaining a sufficientlyhomogeneous layer of expandable graphite. In the case of the binary“water/expandable graphite” mixture, the problem mainly lies in aninstability of the mixture leading to a separation of the phases in thespraying circuit. This instability may in part be corrected byincreasing the viscosity of the dispersing phase, in this case thewater. However, this increase of viscosity of the dispersing phasegenerates difficulties of implementation of spray deposition. In thecase of the binary “polymer binder/expandable graphite” mixture, themain problems are, on the one hand, a problem of dispersion of theexpandable graphite particles in the polymer binder due to theelectrostatic affinities between the two phases, and on the other hand,a spraying problem. To overcome the technical problem linked to spraydeposition and to graphite layer homogeneity, the applicant hasdeveloped a method that consists in firstly depositing an adhesiveprimer layer on thecovering sheets, then depositing, through drydeposition, preferably through fluidized bed spray deposition or throughhopper deposition, a fireproof coating comprising expandable graphite.

Accordingly, the present invention has for object bitumen-impregnatedcellulose fiber sheets, including on at least one of their main surfacesan adhesive primer layer, and, deposited on said adhesive primer layer,a fireproof coating comprising expandable graphite.

Preferably, the adhesive primer layer and the expandable graphite-basedfireproof coating are in direct contact. In a particular embodiment, theadhesive primer layer is in direct contact (i) with the fireproofcoating comprising expandable graphite, and (ii) with thebitumen-impregnated cellulose fiber sheet.

As used herein, “fireproof coating” means a coating that allows a fireprotection of inflammable materials such as bitumen and cellulosefibers, i.e. retarding or stopping the fire propagation and penetration.

The present invention has also for object a method of manufacturingsheets as described hereinabove. Said method comprises (a) depositing anadhesive primer on at least one of the main surfaces of thebitumen-impregnated cellulose fiber sheet, (b) depositing through drydeposition, on the adhesive primer layer, a fireproof coating comprisingexpandable graphite, and optionally, (c) depositing a layer of paint onthe fireproof coating.

The present invention has also for object the use of sheets such asdefined hereinabove as roof covering material.

In the present application, when an article comprises one or severalcoatings on its surface, the phrase “depositing a layer or a coating onthe article” means that a layer or a coating is deposited on theuncovered (exposed) surface of the external coating of the article, i.e.the coating that is the most distant from the substrate.

In the present application, a coating that is “on” a substrate/coatingor that has been deposited “on” a substrate/coating is defined as acoating that (i) is positioned above the substrate/coating, (ii) is notnecessarily in contact with the substrate/coating, that it to say thatone or several intermediate coatings may be arranged between thesubstrate/coating and the coating in question (however, it is preferablyin direct contact with said substrate/coating), and (iii) does notnecessary fully cover the substrate/coating. When “a layer 1 is locatedunder a layer 2”, it means that the layer 2 is more distant from thesubstrate than the layer 1.

According to the invention, the bitumen-impregnated cellulose fibersheets used for the deposition of the adhesive primer and the depositionof the fireproof coating are manufactured according to a method that isperfectly known by the one skilled in the art. This method that isexemplified in the present application comprises the following mainsteps:

-   -   manufacturing a cardboard sheet from cellulose fibers;    -   coating one of the faces of the cardboard sheet with a        thermosetting resin possibly containing pigments;    -   optionally, corrugating the cardboard sheet;    -   drying and cutting the cardboard sheet;    -   deeply impregnating the cardboard sheet with hot bitumen.

According to the invention, the bitumen-impregnated cellulose fibersheets used for the deposition of the adhesive primer and the depositionof the fireproof coating typically comprise 40 to 60 wt. % (weightpercent) of bitumen relative to the total weight of said impregnatedsheets. They typically comprise 40 to 60 wt. % of cellulose fibersrelative to the total weight of said impregnated sheets. They typicallycomprise 0.5 to 2 wt. % of thermosetting resin relative to the totalweight of said impregnated sheets.

In a particular embodiment, the bitumen-impregnated cellulose fibersheets comprise 0.5 to 2 wt. % of pigments relative to the total weightof said impregnated sheets.

In another particular embodiment, they comprise 5 to 12 wt. % of mineralfillers relative to the total weight of said impregnated sheets.

The list of components of the bitumen-impregnated cellulose fiber sheetsgiven hereinabove is of course not limitative.

The bitumen used is a mixture of hydrocarbon materials of natural origincoming from the heavy end obtained upon petroleum distillation, orcoming from natural deposits, in solid or liquid form, of density 0.8 to1.2. Also admitted as bitumens within the meaning of the invention arethe bitumens modified by incorporation of additives of any nature suchas additives for improving the adhesiveness characteristics, forartificially providing the required properties for producing a cationicemulsion, by incorporation of elastomers, in the form of rubber powderor other, or the bitumens improved by addition of polymers of varioustypes; this list being of course not limitative.

The cellulose fibers are typically recycled cellulose fibers coming fromold papers, cardboards or newspapers, for example; the list being notlimitative.

The thermosetting resin is a resin or a mixture of resins preferablychosen from epoxy resins, polyurethane resins, polyurea resins,polyurea-formaldehyde resins, melamine-formaldehyde resins, epoxy vinylester resins or vinyl ester resins; the list being not limitative.

The pigments are preferably metal oxides, such as iron oxide or chromiumoxide; the list being not limitative. The iron oxide allows obtainingalmost all the colors. The role of the pigments is in particular toobtain colored covering sheets that are adaptable to the architecturalenvironment.

The mineral fillers are mainly provided by the grades of recycled oldpaper used to form the paper pulp that serves for manufacturing thebitumen-impregnated cellulose fiber sheets. The mineral fillers aretypically carbonates, silicates and aluminates. In a particularembodiment of the invention, these mineral fillers may be added in therecycled cellulose fibers at the defibration step or at the drainingstep.

In a particular embodiment of the invention, the bitumen-impregnatedcellulose fiber sheets used for the deposition of the adhesive primerand the deposition of the fireproof coating have corrugations intendedin particular to collect water. As described in the patent FR 2,755,712,the corrugations may be of irregular form and substantially sinusoidal.The sheets may also have an alternation of waves and flat regions.Moreover, the corrugations may be different, for example, of thecrenellated or V-shaped type.

In the present invention, the corrugations are preferably sinusoidal.The height of the sinusoidal corrugations is generally of 10 to 100 mm,and preferably of 30 to 45 mm. The ratio between the amplitude and thepitch of the corrugations varies preferably from 1/2 to 1/1.

The basis weight of the bitumen-impregnated cellulose fiber sheetsbefore the deposition of the adhesive primer and the deposition of thefireproof coating is generally higher than 0.8 kg/m², and advantageouslyhigher than 2.6 kg/m².

In the present application, all the basis weights are related to thedeveloped surface of the corrugated sheet. In the case where thecorrugations are parallel to the length of the sheet, the developedsurface of the corrugated sheet is obtained by multiplying the length ofthe corrugated sheet by the developed width of the corrugated sheet,i.e. by the distance following the closest the profile of the sheetcorrugation. In the case where the corrugations are parallel to thewidth of the sheet, the developed surface of the corrugated sheet isobtained by multiplying the width of the corrugated sheet by thedeveloped length of the corrugated sheet, i.e. by the distance followingthe closest the profile of the sheet corrugation.

The thickness of the bitumen-impregnated cellulose fiber sheets beforethe deposition of the adhesive primer and the deposition of thefireproof coating is generally at least of 1.5 mm, preferably higherthan 2 mm, and better, it varies from 2.5 to 3.5 mm.

According to the invention, the bitumen-impregnated cellulose fibersheets described hereinabove are coated with an adhesive primer layerand a fireproof coating comprising expandable graphite.

The adhesive primer has mainly for role to favor the adhesiveness of thefollowing layers in the final product, in particular the adhesion andthe cohesion of the particles of expandable graphite.

Indeed, when the cellulose fiber sheet according to the invention hasjust been impregnated with bitumen and is still hot, the bitumen layerspresent on the main upper and lower surfaces of said sheet are ephemeraland remain only a few seconds. Therefore, said ephemeral bitumen layerscannot serve as adhesive layers to immobilize the fireproof coating, andin particular to immobilize the expandable graphite. This technicalproblem is not observed in the case of roof sheets or membranes based onpolyester and/or polyamide fibers, because, when these latter areimpregnated with bitumen, they have on their main upper and lowersurfaces sufficiently stable bitumen layers that play, when still hot,the role of adhesive layers and allow the immobilization of theexpandable graphite particles.

The adhesive primer preferably comprises a polymer binder. The polymerbinder is preferably a polymer or a mixture of polymers chosen from thethermoplastic resins such as polyvinyl resins, polyvinylidene resins,polyacrylic resins, methacrylic resins or polystyrene resin; the listbeing not limitative. An example of preferred thermoplastic resin is apolymer of the vinyl acetate type.

The adhesive primer layer in the final product corresponds to a drymatter basis weight of generally 10 to 200 g/m2, and preferably of 20 to70 g/m2.

The fireproof coating of the invention comprises expandable graphite.This coating is preferably in direct contact with the adhesive primerlayer. The method of deposition of the fireproof coating comprisingexpandable graphite will be described hereinafter.

The expandable graphite of the present invention has typically acrystalline structure composed of carbon atoms forming planes stackedparallel to each other, in which have been inserted acid molecules, asfor example molecules of sulfuric acid or nitric acid. When theexpandable graphite is exposed to fire or to a flame, the acid moleculesbreak down and generate gas. The pressure of this gas then forces thegraphitic planes to move apart from each other, which generates adilatation of the graphite. The volume of the graphite particles maythen be multiplied by a factor of more than 80 in a few seconds. Thethus-dilated graphite has a low density; it is not combustible and formsa good thermal isolator because it reflects a part of the radiatingheat.

Other known advantages of the expandable graphite are, further, that itis of natural origin, it is not polluting, and it does not dissolve inwater. The expandable graphite serves as a fire-retardant agent due toan endothermic combustion reaction, but above all due to the formationof an isolating barrier after expansion. It also permits to reduce thethermal conductivity of a material. The flame propagation is limited andthe thermal radiation is low. The expandable graphite further guaranteesa low density of the smoke and reduces significantly the dripping of thebitumen binder.

In the present invention, the expandable graphite has preferably anexpansion coefficient higher than 70 cm³/g, and advantageously higherthan 120 cm³/g, when it is exposed to a temperature of 600° C.

The expandable graphite is generally in the form of sprayable flakes.The particle size is typically of 50 to 600 μm, and preferably 150 to400 μm.

Expandable graphite particles are commercially available with a greatnumber of suppliers. They have a “trigger” temperature (temperature atwhich the graphite expansion starts after exposure to a flame during afew seconds) generally ranging from 130° C. to 500° C.

The inflammation temperature of a bitumen-impregnated cellulose fibersheet according to the invention is lower than that of a bitumen sheetor membrane based on polyester and/or polyamide fibers. The inflammationtemperature of a bitumen-impregnated cellulose fiber sheet according tothe invention is typically lower than 300° C., in particular lower than190° C. For example, it is of 130° C. to 270° C. Therefore, theexpandable graphite according to the invention has preferably a triggertemperature lower than 300° C. For example, it is of 120° C., 130° C.,140° C., 150° C., 160° C., 170° C., 180° C., 190° C., 200° C., 210° C.,220° C., 230° C., 240° C., 250° C., 260° C., 270° C., 280° C., 290° C.,300° C. In particular embodiments, it is of 160° C. or 220° C.Particularly satisfying results are obtained for expandable graphitetrigger temperatures ranging from 120° C. to 220° C., in particular from160° C. to 220° C. or from 120° C. to 180° C. Very good results areobtained for a minimum trigger temperature of 160° C. The layer ofexpandable graphite in the final product corresponds to a dry matterbasis weight generally ranging from 50 to 300 g/m², and preferably from80 to 140 g/m². This basis weight corresponds to a “mean basis weight”over the whole developed surface of the sheet according to theinvention. The best results of flame holding and thus fire resistance ofthe sheets according to the invention are obtained when the homogeneityof the expandable graphite distribution is optimum, i.e. when the “localbasis weight” of the layer of expandable graphite in the final productis at least of 80 g/m² in dry matter weight, in any point of said sheet.According to the invention, the term “point” means a developed surfaceranging from 1 cm² to 900 cm² (for example, 30 cm×30 cm, i.e. the sizeof a firebrand used for the fireproof tests described hereinafter), inparticular from 1 cm² to 100 cm², preferably from 1 cm² to 2 cm². Themeasurement of the local basis weight of the expandable graphite may forexample be made by means of adhesive labels whose size corresponds tothe size of the developed surface to be tested (for example, of 2 cm² ifit is desired to test areas having a developed surface ranging from 1cm² to 2 cm²). This measurement is made by differential calculation. Forexample, on the one hand, an adhesive label is applied on abitumen-impregnated cellulose fiber sheet comprising an adhesive primerlayer. The label is removed; which allows taking a sample of theadhesive primer present on the tested area. The quantity of adhesiveprimer is then calculated by weighting the label before and after thesample has been taken. On the other hand, the same operation is carriedout with a label of same size on the same sheet, which furthercomprises, this time, a layer of expandable graphite on the adhesiveprimer layer. This second operation allows quantifying the quantity ofadhesive primer and of expandable graphite present in the tested area.The mass quantification of the expandable graphite is then obtained bydifference between (i) the measurement of the quantity of adhesiveprimer and of expandable graphite, and (ii) the measurement of thequantity of adhesive primer.

In a particular embodiment, the bitumen-impregnated cellulose fibersheet coated with the adhesive primer layer and the fireproof coatingmay also include a layer of paint deposited on the fireproof coating.The layer of paint has for main role to improve the good resistance ofthe graphite over time. It is also used for aesthetic effect. The paintthat can be used in the present invention is typically of vinyl oracrylic nature. The polymer present in the layer of paint is generallythe same as that of the adhesive primer. The layer of paint correspondsto a dry matter basis weight generally ranging from 50 to 300 g/m², andpreferably from 100 to 200 g/m².

The present invention has also for object a method of manufacturingfireproof-treated, bitumen-impregnated cellulose fiber sheets asdescribed hereinabove.

This method comprises (a) depositing an adhesive primer on at least oneof the main surfaces of the bitumen-impregnated cellulose fiber sheetand (b) depositing through dry deposition, on the adhesive primer layer,a fireproof coating including expandable graphite.

In a particular embodiment of the present invention, the methodcomprises a step of depositing a layer of paint on the fireproofcoating.

The deposition of the adhesive primer is carried out through spraydeposition, through coating using further a roll or a brush, or throughany other mode known by the one skilled in the art, the preferred modebeing spraying. This spray deposition is implemented, for example, bymeans of sweeping nozzles such as those conventionally used by the oneskilled in the art for the deposition of a layer of paint on a coveringsheet. An exemplary implementation of the adhesive primer spraydeposition is detailed hereinafter in the present application. Theadhesive primer is sprayed over at least one of the main surfaces of thebitumen-impregnated cellulose fiber sheet, preferably at least thesurface of the sheet having the possibly pigmented thermosetting resinlayer described hereinabove. The nozzles are oriented in such a mannerthat the adhesive primer layer is the most homogeneous possible. Theadhesive primer layer corresponds to a dry matter basis weight generallyranging from 10 to 200 g/m², and preferably from 20 to 70 g/m².

The dry deposition of the fireproof coating comprising expandablegraphite is carried out on a bitumen-impregnated cellulose fiber sheetincluding on at least one of its main surfaces an adhesive primer layer,said sheet having preferably a temperature lower than 160° C., inparticular lower than 120° C. Indeed, the graphite expansion phenomenonof is not reversible, i.e. once the expandable graphite has reached itstrigger temperature, it expands and will not recover its non-expandedinitial state if cooled to a temperature lower than its triggertemperature. During the manufacturing of a bitumen-impregnated cellulosefiber sheet according to the invention, the drying temperature of thecellulose fiber sheet is about 260° C. and the temperature of thebitumen during the step of hot impregnation is about 190° C. The triggertemperature of the expandable graphite according to the invention beingpreferably lower than 300° C., for example ranging from 120° C. to 180°C. or from 160° C. to 220° C., for the hereinabove-mentioned reasons ofinflammation temperature of the sheet according to the invention, theexpandable graphite can be deposited only after the step of drying thecellulose fiber sheet and hot impregnation with bitumen. The expansionof the expandable graphite is thus avoided during the manufacturing ofthe sheet according to the invention and before the use of said sheet asa fireproof roof covering.

The dry deposition of the fireproof coating comprising expandablegraphite is preferentially carried out through gravity deposition, inparticular through hopper deposition, or through spray deposition, andadvantageously through fluidized bed spray deposition of the expandablegraphite. The fluidized bed spray deposition of the expandable graphiteis preferred to the hopper deposition because it allows obtaining alayer of expandable graphite that is more homogeneous and thus morefire-resistant.

The gravity deposition, in particular hopper distribution, consists incarrying the sheet having the adhesive primer layer as definedhereinabove, under a hopper (or tank) filled with the expandablegraphite; the surface of the sheet having the adhesive primer layerbeing exposed to the hopper so that the deposition of the expandablegraphite is carried out on the adhesive primer layer. The hopper ispreferably equipped, at the lower end, with a knurled roll, whose speedand position relative to the hopper wall (corresponding to the lipopening size) may be varied, the knurled roll serving to distribute thegraphite as a function of the required quantities and of the speed ofadvance of the sheet. The knurled roll also allows obtaining a betterdistribution of the expandable graphite and thus improving the fireresistance of the sheet according to the invention.

The fluidized bed spraying of the expandable graphite consists inputting the expandable graphite in suspension in a gas flow swirl insuch a way that the expandable graphite, which is a solid, behaves as aliquid. The dry particles of expandable graphite are placed in afluidized bed container. The gas flow is preferentially injected underthe particles of expandable graphite, so as to propel the particles inthe gas flow swirl and to form a cloud of particles in suspension in thegas flow. The gas flow used in the present invention is preferentially aflow of air having a pressure varying from 2 to 3 Bar, and still bettera pressure of 2.5 Bar. The suspension of expandable graphite in the gasflow is then sprayed over the main surface of the sheet having theadhesive primer layer. The spraying is preferably carried out by meansof nozzles having an opening that is preferably not circular and whosesurface area varies from 45 to 60 mm², preferably from 50 to 52 mm², andstill better of 51.17 mm². A flow of air of 2 to 3 Bar allows a flowrate of dry particles of expandable graphite varying from 400 to 500g/min per nozzle. The quantity of expandable graphite deposited dependson the quantity and the nature of the polymer binder of the hereinabovedefined adhesive primer layer. For example, for an adhesive primer layercontaining vinyl acetate and corresponding to a dry matter basis weightranging from 20 to 70 g/m², the quantity of expandable graphitedeposited varies from 80 to 140 g/m². The dry deposition of theexpandable graphite is preferably carried out until physical saturationof the surface of the adhesive primer layer. The excess of expandablegraphite is then eliminated by blowing. On the sheet, there thus remainonly the particles of expandable graphite in contact with the adhesiveprimer layer.

The deposition of the layer of paint is carried out through spraydeposition, through coating using further a roll or a brush, or throughany other mode known by the one skilled in the art, the preferred modebeing spray deposition. This spray deposition is implemented, forexample, by means of sweeping nozzles such as those conventionally usedby the one skilled in the art for the deposition of a layer of paint ona covering sheet. The layer of paint corresponds to a dry matter basisweight generally ranging from 50 to 300 g/m², and preferably from 100 to200 g/m².

The present invention has also for object a bitumen-impregnatedcellulose fiber sheet obtainable by the method according to theinvention.

The present invention has also for object the use of abitumen-impregnated cellulose fiber sheet as defined in the presentinvention as a roof covering material. Generally, thebitumen-impregnated cellulose fiber sheets of the present invention canbe used in the building industry, in the construction or renovation ofroofs. The sheets according to the invention can be used, for example,as roof accessories, such as, without being limited thereto, ridgetiles, border tiles and skylight frames.

The examples hereinafter illustrate the present invention withoutlimiting the latter.

EXAMPLES

A) Bitumen-Impregnated Cellulose Fiber Sheets Used for the Deposition ofthe Adhesive Primer and that of the Fireproof Coating

a. Materials

Examples of sheets are Onduline CLASSIC®, Onduline ONDUTOIT®, OndulineONDUVILLA® or Onduline DURO235® sheets, manufactured by the ONDULINECompany. All these sheets have a basis weight higher than 2.6 kg/m²,except the ONDUTOIT® sheets, which have a basis weight of 2.2 kg/m². Theonduline CLASSIC® sheets are corrugated sheets having a weight of 6.4kg, a length of 200 cm, a width of 95 cm, a thickness of 3 mm, andcorrugations with a height of 38 mm.

The Onduline ONDUTOIT® sheets are corrugated sheets ideal for coveringsmall storage facilities (industrial and agricultural), ancillary andleisure facilities. These are single-layer bitumen sheets, pigmented indepth, with a thermosetting resin. The sheets have a length of 200 cm, awidth of 95 cm, a thickness of 2.60 mm, a wave depth of 38 mm, a wavepitch of 95 mm, a wave number of 9 to 10, and a mass of 5.60 kg. Theirbursting resistance when in dry-state is 17 bars.

The Onduline ONDUVILLA® sheets are corrugated tiles having a thicknessof 3 mm, a wave depth of 40 mm, a length of 40 cm and a width of 106 cm.Also included in the sheet examples are the sheets having the samethickness and the same wave depths than the Onduline ONDUVILLA® tiles,but having a length of 200 cm and a width of 106 cm.

The Onduline DURO 235° sheets are corrugated sheets ideal for coveringsmall storage facilities (industrial and agricultural), ancillary andleisure facilities. These are single-layer bitumen sheets, pigmented indepth, with a thermosetting resin. The sheets have a length of 200 cm, awidth of 95 cm, a thickness of 3.00 mm, a wave depth of 38 mm, a wavepitch of 95 mm, a wave number of 10, and a mass of 6.75 kg. Theirbursting resistance when in dry-state is 19 bars.

The Onduline CLASSIC®, Onduline ONDUTOIT®, Onduline ONDUVILLA® andOnduline DURO 235®sheets contain 44 wt. % of cellulose fibers, 8 wt. %of mineral fillers, 46 wt. % of bitumen, 1 wt. % of thermosetting resinand 1 wt. % of pigment.

b. Manufacturing Method

An example of method of manufacturing said sheets comprises thefollowing steps, which are well known by the one skilled in the art:

-   -   manufacturing a paper pulp from old papers, from which all        foreign scraps, such as plastic for example, have been removed;    -   applying the paper pulp on a flat table for a natural draining        of the pulp;    -   sucking and pressing the paper pulp in order to obtain cardboard        sheet    -   roll-coating, on one of the faces of the cardboard sheet, a        thermosetting resin containing pigments such as iron oxide or        chromium oxide;    -   mechanically corrugating the cardboard sheet;    -   drying and cutting the cardboard sheet;    -   deeply impregnating the cardboard sheet with hot bitumen.

B) Polymers Used for the Adhesive Primer

Examples of adhesive primer compositions used in the present inventionare 40% vinyl acetate aqueous emulsions. The vinyl acetate is, forexample, Axilat AOD 515, marketed by the Hexion Company, or Mowilith LDM1851 marketed by the Celanese Company. Axilat AOD 515, which isgenerally used for paint formulations, is marketed in the form of a 50%aqueous emulsion. In the present invention, it is thus diluted to 40%before application.

C) Expandable Graphite Used for the Fireproof Coating

Non-limitative examples of expandable graphite particles used in thepresent invention are the expandable graphite PX200 or PX85, marketed bythe Alphamin Company, or the expandable graphite S90 or S7, marketed bythe Netexium Company. By way of example, the PX85 particles comprise 95wt. % of carbon, 4 wt. % of ash, 0.5 wt. % of free acids and 6.8 wt. %of sulfates. Those particles have a pH of 3 to 7. They have an expansioncoefficient of 200 cm³/g and 80% of them have a nominal size of 180 μm.

Typical examples of particles that can be used for the present inventionare particles of grades 160-80, 160-50, 220-80 or 220-50. The firstnumber indicates the temperature in degrees Celsius at which thegraphite expansion starts, and the second number corresponds to the sizeof the particles, in Mesh.

D) Paint Used for the Layer of Paint

An example of preferred paint used in the present invention is the paintISOLA manufactured by Onduline. Other examples of paint are allaqueous-phase outdoor paints for wood.

E) Methods of Manufacturing a Bitumen-Impregnated Cellulose Fiber SheetIncluding an Adhesive Primer Layer, a Fireproof Coating and a Layer ofPaint

Abitumen-impregnated cellulose fiber sheet of the Onduline CLASSIC®,Onduline ONDUTOIT®, Onduline ONDUVILLA® or Onduline DURO235® type,manufactured by the ONDULINE Company and as described hereinabove, isplaced on an automated conveyor belt, in such a manner that the exposedsurface is the surface having the layer of pigmented thermosettingresin.

The conveyor belt carries the sheet into a first stainless-steelchamber, equipped with sweeping nozzles containing the adhesive primer.In the present example, the adhesive primer is a 40% vinyl acetateaqueous emulsion, of the Axilat AOD 515 type. The emulsion is sprayedover the exposed surface of the sheet, i.e. on the surface having thelayer of pigmented thermosetting resin. The sweeping nozzles areoriented in such a manner that the adhesive primer layer is the mosthomogeneous possible. The adhesive primer layer corresponds to a drymatter basis weight of 50 g/m².

After the deposition of the adhesive primer, the conveyor belt carriesthe sheet outside the first chamber so that the one skilled in the artchecks the deposited layer.

Before the adhesive primer layer dries, the conveyor belt carries thesheet into a second chamber for performing the deposition of thefireproof coating. The expandable graphite used is, for example, PX200of PX85, marketed by Alphamin, or S90 or S7, marketed by Netexium.

In the case of hopper deposition, the chamber comprises a hopperequipped, at the lower end, with a knurled roll, whose speed may bevaried and which serves to distribute the graphite as a function of therequired quantities and of the speed of advance of the sheet. Forexample, to deposit on a sheet 100 g/m² of dry expandable graphite, at arate of 500 sheets per hour, the linear speed of the conveyor belt isadjusted between 15 m/min and 20 m/min, preferably 18 m/min, the speedof the 85 mm diameter knurled roll being adjusted from 20 rpm to 30 rpm,preferably 26 rpm, and the relative position of the knurled roll withrespect to the hopper wall is adjusted so as to obtain a lip opening of0 mm to 1 mm, preferably 0.1 mm.

In the case of fluidized bed spray deposition, the chamber is equippedwith 8 nozzles having each an opening of 51.17 mm². The nozzles areconnected to a fluidized bed container containing the expandablegraphite and a system for creating a flow of air.

The dry particles of expandable graphite placed in the fluidized bedcontainer are put in suspension in an air flow swirl before beingsprayed by the nozzles over the surface of the covering sheet having thenon-dried adhesive primer layer. The flow of air is injected under theparticles of expandable graphite so as to propel them in the gaseousflow swirl and to form a cloud of particles in suspension in the gaseousflow. The flow of air is of 2.5 Bar and allows a flow rate of dryparticles of expandable graphite of 455 g/min per nozzle, i.e. a totalflow rate of dry particles of expandable graphite of 3640 g/min for 8nozzles. The layer of expandable graphite in the final productcorresponds to a dry matter basis weight of at least 80 g/m² in anypoint of the sheet having a developed surface ranging from 1 cm² to 2cm².

After the deposition of the fireproof coating comprising the expandablegraphite, the conveyor belt carries the sheet out of the second chamberso that the one skilled in the art checks the deposited layer.

The sheet is then possibly carried into a third stainless-steel chamberfor the deposition of a layer of paint. The third chamber is equippedwith sweeping nozzles conventionally used by the one skilled in the artfor the deposition of paint on the covering sheets. The paint used isthe paint ISOLA from ONDULINE. It is sprayed through the nozzles overthe previously deposited layer of fireproof coating. The layer of paintcorresponds to a dry matter basis weight ranging from 140 to 150 g/m².

F) Tests of Resistance of the Sheets According to the Invention to anExternal Fire According to the Standard EN 13 501-5

The European Standard EN 13 501-5 allows for a fire classification ofthe construction products and building elements as a function of theirfire resistance. The test methods used to test the roofs exposed to anexternal fire are defined in the Standard XP ENV 1187. This Standardcontains four types of tests:

-   -   Test 1 is performed with inflamed firebrands (baskets). It is        based on the German Standard DIN 4102-7;    -   Test 2 is performed with inflamed firebrands in the presence of        wind. It is based on the Scandinavian Standard Nordtest NT Fire        006;    -   Test 3 is performed with inflamed firebrands in the presence of        wind and radiating heat. It is based on the order of Sep. 10,        1970, of the French Ministry of Interior. It defines the classes        and index T30/1;    -   Test 4 is performed in two steps with inflamed firebrands in the        presence of wind and radiating heat. It is based on the British        Standard BS 476/3.

Each test is independent. There exists no predetermined order to performthem. Each test defines the criteria that must be met by the sheetssubjected to an external fire as well as the conditions in which thesheets are tested.

Only Tests 1 and 3 are detailed hereinafter. However, the sheetsaccording to the invention have responded positively to Tests 2 and 4.

a. Tests 1

Tests 1 have been carried out with corrugated sheets having a length of1.8 m, a width of 0.8 m, a thickness of 3 mm, and corrugations with aheight of 38 to 40 mm. The sheets contain 44 wt. % of cellulose fibers,8 wt. % of mineral fillers, 46 wt. % of bitumen, 1 wt. % ofthermosetting resin and 1 wt. % of pigment. Some sheets have been testedas such, i.e. with no adhesive primer layer and no fireproof coating;they are called hereinafter “sheets without fireproof coating”. Theyconstitute the test specimens of Tests 1 and 3. Sheets according to theinvention, called hereinafter “sheets with fireproof coating”, have beentested with the following coatings:

-   -   an adhesive primer layer comprising vinyl acetate (Axilat AOD        515), having a dry matter basis weight of 30 to 50 g/m²,    -   a fireproof coating comprising expandable graphite of the PX85        type, having a local dry matter basis weight of about 100 g/m²        in any point having a developed surface ranging from 1 cm² to 2        cm²,    -   a layer of vinyl paint of the ISOLA type, having a dry matter        basis weight of 140 g/m² to 150 g/m².

The conditions of Test 1 are the following:

-   -   the slope of the roof is 15° or 45°,    -   the firebrand is a basket of 300 mm×300 mm×200 mm with 600 g of        pine straw,    -   the test is stopped after the fire is totally stopped.

The sheets responding positively to the test are classified B_(roof) andthose responding negatively to the test are classified F_(roof).

The following Table presents the results of Test 1.

Sheets without Sheets with Criteria of fireproof fireproof Main CriteriaClassification coating coating Upward external fire <0.7 m >0.7 m (fire)<0.7 m propagation Maximum burned length <0.8 m >0.8 m (fire) <0.8 mIncandescent points None Fire under the Non penetrating the roof sheetFire Classification B_(roof) F_(roof) B_(roof)b. Tests 3

Tests 3 have been carried out with sheets similar to those used forTest 1. The only criteria that change are the length of the sheets,which is then of 2 m instead of 1.8 m, and the width of the sheets,which is of 1.2 m instead of 0.8 m.

The conditions of Test 3 are the following:

-   -   the slope of the roof is fixed to 30°,    -   the firebrand is a wood-fiber basket of 55 mm×55 mm×32 mm,        impregnated with n-heptane,    -   the wind is applied at a speed of 3 m/s,    -   the radiating panel providing the radiating heat has a power of        12.5 kW/m²,    -   the test is stopped after the fire is totally stopped.

The sheets responding positively to Test 3 are classified B_(roof),C_(roof) or D_(roof) according to their degree of resistance, the sheetsB_(roof) being the most performing and the sheets D_(roof) being theless performing. The sheets responding negatively to the test areclassified F_(roof).

The following Table presents the results of Test 3.

Sheetswithout Sheets with Main fireproof fireproof Criteria Criteria ofClassification coating coating Time of TE > 30 TE > 10 TE > 10 TE < 5TE > 30 external min min min min min fire propagation (TE) Time TP > 30TP > 15 TP > 5 TP < 5 TP > 30 untilfire- min min min min min penetrationFire B_(roof) C_(roof) D_(roof) F_(roof) B_(roof) Classi- fication

The results of Tests 1 and 3 show that the cellulose fiber sheetsaccording to the present invention respond correctly to the differentcriteria of fireproof classification of the Standard EN 13501-5,contrary to the sheets having no fireproof coating.

Other tests have shown that the sheets processed according to theinvention had a very good aging ability (UV exposure, frost/thaw cycles,wet abrasion).

The dry deposition of expandable graphite, and in particular fluidizedbed spray deposition or hopper deposition, is thus a performing methodto obtain a layer of expandable graphite that is sufficientlyhomogeneous to obtain the desired result, which is to improve the fireresistance.

1. A bitumen-impregnated cellulose fiber sheet, comprising on at leastone of its main surfaces an adhesive primer layer, characterized in thata fire proof coating comprising expandable graphite is deposited on thisadhesive primer layer.
 2. The bitumen-impregnated cellulose fiber sheetaccording to claim 1, characterized in that it includes corrugations. 3.The bitumen-impregnated cellulose fiber sheet according to claim 1,characterized in that the expandable graphite has an expansioncoefficient higher than 120 cm³/g at 600° C.
 4. The bitumen-impregnatedcellulose fiber sheet according to claim 1, characterized in that theexpandable graphite has a trigger temperature lower than 300° C.
 5. Thebitumen-impregnated cellulose fiber sheet according to claim 1,characterized in that the expandable graphite has a trigger temperatureranging from 160° C. to 220° C.
 6. The bitumen-impregnated cellulosefiber sheet according to claim 1, characterized in that the mean drymatter basis weight of expandable graphite varies from 80 to 140 g/m².7. The bitumen-impregnated cellulose fiber sheet according to claim 1,characterized in that the local dry matter basis weight of expandablegraphite is at least of 80 g/m² in any point having a developed surfaceranging from 1 cm² to 900 cm².
 8. The bitumen-impregnated cellulosefiber sheet according to claim 7, characterized in that the local drymatter basis weight of expandable graphite is at least of 80 g/m² in anypoint having a developed surface ranging from 1 to 2 cm².
 9. Thebitumen-impregnated cellulose fiber sheet according to claim 1,characterized in that it includes a layer of paint deposited on thefireproof coating.
 10. A method of manufacturing a bitumen-impregnatedcellulose fiber sheet according to claim 1, comprising (a) depositing anadhesive primer on at least one of the main surfaces of thebitumen-impregnated cellulose fiber sheet, (b) depositing through drydeposition, on the adhesive primer layer, a fireproof coating comprisingexpandable graphite.
 11. The method according to claim 10, furthercomprising (c) depositing a layer of paint on the fireproof coating. 12.The method according to claim 10, characterized in that the fireproofcoating is deposited by fluidized bed spray deposition.
 13. The methodaccording to claim 10, characterized in that the fireproof coating isdeposited by hopper deposition.
 14. The method according to claim 13,characterized in that the fireproof coating is deposited through ahopper equipped, at the lower end, with a knurled roll.
 15. Method ofcovering a roof which comprises: providing a bitumen-impregnatedcellulose fiber sheet according to claim 1; and applying said sheet tothe roof as a roof covering material.
 16. The bitumen-impregnatedcellulose fiber sheet according to claim 2, characterized in that theexpandable graphite has an expansion coefficient higher than 120 cm³/gat 600° C.
 17. The bitumen-impregnated cellulose fiber sheet accordingto claim 2, characterized in that the expandable graphite has a triggertemperature lower than 300° C.
 18. The bitumen-impregnated cellulosefiber sheet according to claim 2, characterized in that the mean drymatter basis weight of expandable graphite varies from 80 to 140 g/m².19. The bitumen-impregnated cellulose fiber sheet according to claim 2,characterized in that the local dry matter basis weight of expandablegraphite is at least of 80 g/m² in any point having a developed surfaceranging from 1 cm² to 900 cm².